Weekly Contest 117

965. Univalued Binary Tree

A binary tree is univalued if every node in the tree has the same value.

Return true if and only if the given tree is univalued.

Example 1:

Input: [1,1,1,1,1,null,1]
Output: true

Example 2:

Input: [2,2,2,5,2]
Output: false

Note:

1. The number of nodes in the given tree will be in the range [1, 100].
2. Each node's value will be an integer in the range [0, 99].

Code:

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    bool isUnivalTree(TreeNode* root) {
        solve(root, root->val);
        return ans;
    }
    
    void solve(TreeNode* root, int num) {
        if (root->val != num) ans = false;
        if (root->left != NULL) solve(root->left, num);
        if (root->right != NULL) solve(root->right, num);
    }
    
private:
    bool ans = true;
};

　　

967. Numbers With Same Consecutive Differences

Return all non-negative integers of length N such that the absolute difference between every two consecutive digits is K.

Note that every number in the answer must not have leading zeros except for the number 0 itself. For example, 01 has one leading zero and is invalid, but 0 is valid.

You may return the answer in any order.

Example 1:

Input: N = 3, K = 7
Output: [181,292,707,818,929]
Explanation: Note that 070 is not a valid number, because it has leading zeroes.

Example 2:

Input: N = 2, K = 1
Output: [10,12,21,23,32,34,43,45,54,56,65,67,76,78,87,89,98]

Code:

class Solution {
public:
    vector<int> numsSameConsecDiff(int N, int K) {
        vector<int> ans;
        if (N == 1) {
            for (int i = 0; i < 10; ++i) 
                ans.push_back(i);
            return ans;
        }
        for (int i = 1; i < 10; ++i) {
            string s = to_string(i);
            dfs(s, N, K, ans);
        }
        return ans;
    }
    
    void dfs(string s, const int N, const int K, vector<int>& ans) {
        if (s.length() == N) {
            ans.push_back(stoi(s));
            return ;
        }
        int lastNum = s[s.length()-1] - '0';
        int temp = lastNum + K;
        string dummy = s;
        if (temp >= 0 && temp < 10) {
            dummy += to_string(temp);
            dfs(dummy, N, K, ans);
        }
        if (K != 0) {
            int temp = lastNum - K;
            if (temp >= 0 && temp < 10) {
                s += to_string(temp);
                dfs(s, N, K, ans);
            }
        }
    }
};

　　

966. Vowel Spellchecker 

Given a wordlist, we want to implement a spellchecker that converts a query word into a correct word.

For a given query word, the spell checker handles two categories of spelling mistakes:

• Capitalization: If the query matches a word in the wordlist (case-insensitive), then the query word is returned with the same case as the case in the wordlist.
  • Example: wordlist = ["yellow"], query = "YellOw": correct = "yellow"
  • Example: wordlist = ["Yellow"], query = "yellow": correct = "Yellow"
  • Example: wordlist = ["yellow"], query = "yellow": correct = "yellow"
• Vowel Errors: If after replacing the vowels ('a', 'e', 'i', 'o', 'u') of the query word with any vowel individually, it matches a word in the wordlist (case-insensitive), then the query word is returned with the same case as the match in the wordlist.
  • Example: wordlist = ["YellOw"], query = "yollow": correct = "YellOw"
  • Example: wordlist = ["YellOw"], query = "yeellow": correct = "" (no match)
  • Example: wordlist = ["YellOw"], query = "yllw": correct = "" (no match)

In addition, the spell checker operates under the following precedence rules:

• When the query exactly matches a word in the wordlist (case-sensitive), you should return the same word back.
• When the query matches a word up to capitlization, you should return the first such match in the wordlist.
• When the query matches a word up to vowel errors, you should return the first such match in the wordlist.
• If the query has no matches in the wordlist, you should return the empty string.

Given some queries, return a list of words answer, where answer[i] is the correct word for query = queries[i].

Example 1:

Input: wordlist = ["KiTe","kite","hare","Hare"], queries = ["kite","Kite","KiTe","Hare","HARE","Hear","hear","keti","keet","keto"]
Output: ["kite","KiTe","KiTe","Hare","hare","","","KiTe","","KiTe"]

Note:

• 1 <= wordlist.length <= 5000
• 1 <= queries.length <= 5000
• 1 <= wordlist[i].length <= 7
• 1 <= queries[i].length <= 7
• All strings in wordlist and queries consist only of english letters.

Code:

class Solution {
public:
    vector<string> spellchecker(vector<string>& wordlist, vector<string>& queries) {
        unordered_map<string, vector<string>> seen, tran;
        unordered_set<string> matches;
        for (int i = 0; i < wordlist.size(); ++i) {
            string temp_tolower = _tolower(wordlist[i]);
            string temp_todev = _todev(wordlist[i]);
            seen[temp_tolower].push_back(wordlist[i]);
            tran[temp_todev].push_back(wordlist[i]);
            matches.insert(wordlist[i]);
        }
        vector<string> ans;
        for (int i = 0; i < queries.size(); ++i) {
            // match 
            if (matches.count(queries[i])) {
                ans.push_back(queries[i]);
                continue;
            }
            
            string temp = _tolower(queries[i]);
            
            // capitalization
            if (seen.count(temp)) {
                ans.push_back(seen[temp][0]);
                continue;
            }
            
            // vowel errors
            string ant = _todev(queries[i]);
            if (tran.count(ant)) {
                ans.push_back(tran[ant][0]);
            } else {
                ans.push_back("");
            }
        }
        
        return ans;
    }

    string _tolower(string s) {
        for (auto& c : s) 
            c = tolower(c);
        
        return s;
    }
    
    string _todev(string s) {
        s = _tolower(s);
        for (auto& c : s)
            if (c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u')
                c = '#';
        return s;
    }
};

　　

In this question I reference the function of _todev with @lee215. 

968. Binary Tree Cameras

Given a binary tree, we install cameras on the nodes of the tree. 

Each camera at a node can monitor its parent, itself, and its immediate children.

Calculate the minimum number of cameras needed to monitor all nodes of the tree.

Example 1:

Input: [0,0,null,0,0]
Output: 1
Explanation: One camera is enough to monitor all nodes if placed as shown.

Example 2:

Input: [0,0,null,0,null,0,null,null,0]
Output: 2
Explanation: At least two cameras are needed to monitor all nodes of the tree. The above image shows one of the valid configurations of camera placement.

Note:

1. The number of nodes in the given tree will be in the range [1, 1000].
2. Every node has value 0.

Code:

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    int minCameraCover(TreeNode* root) {
        int state = dfs(root);
        return res + (state < 1 ? 1 : 0);
    }
    
    int dfs(TreeNode* root) {
        int needCamera = 0;
        int covered = 0;
        
        if (root->left == NULL && root->right == NULL) 
            return 0;
        
        if (root->left != NULL) {
            int state = dfs(root->left);
            if (state == 0) {
                needCamera = 1;
                covered = 1;
            } else if (state == 1) {
                covered = 1;
            }
        } 
        
        if (root->right != NULL) {
            int state = dfs(root->right);
            if (state == 0) {
                needCamera = 1;
                covered = 1;
            } else if (state == 1) {
                covered = 1;
            }
        } 
        
        if (needCamera > 0) {
            res++;
            return 1;
        }
        
        if (covered > 0) {
            return 2;
        }
        
        return 0;
    }
    
private:
    int res = 0;
};

　　

Analysis:

https://leetcode.com/problems/binary-tree-cameras/discuss/211180/JavaC%2B%2BPython-Greedy-DFS